Why are some DVDs louder than others?

I’m not talking about the movies themselves, but the noise the DVD player makes when playing them. Some DVDs make a loud whirring or knocking sound that I can hear across the room, whereas others are very silent. Off the top of my head, every season of Monk does this. I have a pretty cheap DVD player, but if that was the reason, I’d expect every DVD to be noisy. What’s the reason for this?

It’s probably just a little less balanced than the other DVDs. Even something as simple as having more print on one side of the label can make a small difference at 2,000 RPM.

Also, discs that are scratched a bit will have to spin slower, possibly resulting in less ‘whirr’.
However, the laser might have to go back and forth over the same area again and again to properly read the data, resulting in more ‘knock’. Also agree that imbalance can make a difference. Cheap media (burned DVDs) will also affect how much seeking the read laser has to do.

At 1600 rpm, the outer edge of a 12cm diameter DVD is feeling a force of 172 g’s.

Well, I don’t think it’s scratches on the DVDs in my case, because the Monk ones at least were doing it new out of the box. It may be the balance issue though.

Thanks

Cite?

Is there a point in making a DVD player that can spin discs considerably faster than you need to to stream data off of them? Especially if you have to slow down for a scratched disk, the one case where you might want to be able to read ahead and build up a buffer.